Multiple copy transfer process and apparatus



N v. '12, 1957 R. w. GUNDLACH 2,812,70

MUL TIPLE COPY TRANSFER PROCESS AND APPARATUS Filed 001;. 21, 1955 2 Sheets-Sheet 1 TRANSFER PARTIAL REMOVAL TRANSFER PARTIAL TO TRANSFER OF TO WEB BACK REMOVAL TRANSF E R OF COPY NEW WEB BACK COPY FIG! HIGH VOLTAGE A JI- SOURCE HIGH VOLTAGE souRcE IN V EN TOR.

ROBERT w. GUNDLACH F I G 4 BY N f ATTORNEY Nov. 12, 1957 RLw. GUNDLACH 2,812,709 7 MULTIPLE COPY TRANSFER PROCEsS AND APPARATUS I Filed Oct.- 21, 1953 2 Sheets-Sheet 2 POSITIVE HMSOURCE PosITIvE H.V.SOURCE NEGATIVE J f a e A I-I.v.souRcE 36 36a. 36 b NEGATIVE H.V.SOURCE POSITIVE H.V.SOURCE PosITIvE NEGATIVE H.V.$OURCE I H.V.$OURCE 4 J F IG. 5

INVENTOR.

ROBERT W. GUNDLACH ATTORNEY United totes Patent Office MULTIPLE TRANSFER PROCESS AND APPARATUS RobereW. Gundiach, Rochester, N. Y., assignor to The halozd Company, Rochester, N. Y a corporation of New York Application Qctoher 21, 1953, Serial No. 337,469 8 Claims. (Cl. 101426) This invention relates in general to the transfer of an image body and in particular to an electrostatic transfer apparatus and method particularly suited to the making of a plurality of transfers or prints from a single electrostatically adhering image body.

In conventional xerographic practice it is usual to form an electrostatic latent image or electrostatic charge pattern on an insulating or photoconductive insulating surface and thereafter utilize this image, for example by deposi tion of an electroscopic material thereon. This electroscopic material, which may be powder particles or the like, adheres electrostatically to the image on the insulating or photoconductive insulating surface and may be transferred to a subsequent surface to yield a xerographic print. According to conventional methods, it is usual to form an electrostatic latent image and develop it by deposition of powder thereon followed by transfer of substantially all the powder, whereby a single xerographic print is formed from a single electrostatic latent image.

New in accordance with the present invention, a single electrostatic latent image or electrostatic charge pattern is utilized for the formation of a plurality of visible im ages or prints. The new result is accomplished by a plurality of cycles or series of steps, in each of which an image body is reversed or mirror configuration is transferred from an image bearing surface to a transfer web and im mediately back to the original surface, without intermediate separation of the two surfaces, followed thereafter by separation to yield on the transfer web a residual image which is the residue after the reverse transfer and which image corresponds to an electrostatic print such as a xerographic print.

The invention is generally illustrated in the following specification and drawings wherein:

Figure 1 is a block diagram of a printing process according to one embodiment of the invention;

Figure 2 is a diagrammatic perspective view of a xerographic plate with an image bearing web member partially removed therefrom;

Figure 3 is a diagrammatic view of apparatus and process stages, according to the invention for the formation of one of a series of multiple copies;

Figure 4 is a diagrammatic view of apparatus according to another embodiment of the invention;

Figure 5 is a diagrammatic view of a continuous machine for production of multiple copies according to this invention.

For purposes of clearer explanation the present invention will be described in terms of xerography, for which it is particularly suited, but it is to be realized that the invention is not necessarily limited thereto. In the preliminary steps from which the present invention follows it is usual in xerography according to present commercial methods to form an electrostatic latent image on a xerographic plate and thereafter develop this image by exposure to an electroscopic material. Thus, for example, a xerographic plate comprising of a photoconductive insulating layer 11 overlying a conductive backing mem- 2,812,709 Patented Nov. 12, 1957 ber 12 may be charged to a relatively uniform electrostatic charge or potential and this charge selectively dissipated by exposure to a pattern of light and shadow whereupon there results an electrostatic charge pattern corresponding to the shadow pattern of the image. Thus, in the areas of exposure to light the original electrostatic charge is selectively dissipated generally in proportion to the exposure, whereas in the unilluminated areas this charge is substantially retained. The resulting image pat tern, comprising charged image areas and relatively uncharged background or non-image areas, is capable of receiving and holding an electroscopic material when developed by the methods shown in Carlson U. S. Patent 2,297,691, Wise Patent 2,618,552, or other convenient methods of development. The result is a developed image 14, herein called an image body, comprising electroscopic material electrostatically adhering to the surface of the Xerographic plate.

According to one embodiment of the present invention as shown in Figures 2 and 3, the image to be reproduced is applied to the xerographic plate by suitable means such as to produce on the plate this image body 14 in right reading or non-mirror image configuration. This image body may thereupon be transferred to a transfer web material as shown in Figures 2 and 3 leaving a mirror image body 15 of developer material on the original transfer web 16. For convenience in subsequent understanding, the resulting product comprising developed image body on the transfer web will be known as the idler sheet.

According to a similar embodiment shown in Figure 4, the image may be formed in mirror-reading configuration on the xerographic plate, whereby the mirror-reading image body 15 on the plate is the master image body for the multiple printing.

The idler sheet bearing the mirror image body then is placed face to face with a subsequent transfer web or copy web 17 and an electrostatic charge or field is applied between these two webs by suitable means such as, for example the deposition of corona discharge on either the idler or transfer web, the polarity being such as to transfer the image body from the idler to the transfer web. Next and without separating the transfer web from the idler, a field of opposite polarity is applied between the two members. For example, by deposition of the charge or opposite polarity on the same surface, or by deposition of a charge of like polarity on the opposite surface or if desired, by other suitable means of applying an electric field between the two members.

After the dual transfer step, wherein the image body is transferred from the idler to the transfer web and back to the idler the two members namely idler and transfer web are separated. The preponderance of the image body has been retransferred to the idler but a substantial but small portion of the image body stays with the transfer web in the form of a residual image thereon. This residual image 19 is a right reading image corresponding to the original optical image and is supported on the transfer web to yield a xerographic print or copy corresponding to the original image being reproduced. This copy then may be fixed or made permanent by suitable methods such as, for example, heat or solvent fusing in the case of an appropriate fusible or by the application of a fixing or protective coating thereover. The resulting copy is the first of a series of multiple copies to be produced by repeating the steps of transfer to the transfer web, reverse transfer of the predominant proportion of the image back to the idler and separation of the two webs and fixing or fusing of the image left on the transfer web.

In Figure 4 is shown diagrammatically the double transfer operation which results in the ultimate partial transfer of an image body from an image bearing surface to a transfer web. In this case the transfer being shown to take place from the'original xerographic plate directly to the ultimate copy support for the formation of one of a series of multiple xerographic prints directly from such xerographic plate. As shown in this figure, an image body T4 is present on a xerographic plate 19 consisting of a photoeonductiv'e insulating layer it overlying a conductive bacliing member 12. This image body 14 has been placed thereon by conventional steps of xerography such as explained hereinbefore including for example, charging the xerographic plate with an electrostatic charge selectively dissipating the charge by exposure to a pattern of light and shadow and subsequently developing the charge pattern areas by deposition of the image body 14 thereon. This image body in the particular embodiment here described may be considered to consist of finely divided negatively charged powder particles adhering to the positive polarity electrostatic latent image residing on the photoconductive insulating layer ll of the xerographic plate. The composite body comprising the xerographic plate 1.2 the transfer Web 17 and the image body 14 therebetween is passed first beneath a positive transfer member, in this case being shown as a transfer roller 23 which is operably connected to the positive terminal 24 of a high voltage source 26. At this transfer member 23 it is observed that the preponderance of the image body is transferred to the transfer web 17 forming thereon an image body 14a which may represent about 68% to about 95% of the original image body 14. By adjustment of the potential of the high voltage source 26 in relation to the charge of the individual powder particles of the image body 14 and in relation to the charge on the xerographic plate 12, a certain degree of control can be exerted as to the proportion of the image body which is transferred to the transfer web in general about 80 to 85% of the image body will be transferred and by increasing the charging effect of transfer member 23 up to about 90 or some instances almost 95% of the image body can thus be transferred. If however, transfer of substantially less than about 60% of the original image body is attempted, the result is uneven transfer with substantially more being transferred in some areas and substantially less in some others. Therefore, in order to achieve satisfactory copy it is recommended that about 80 to 85% of the image body be transferred from the plate i2 to the transfer web 17 leaving therefore in the order of to of the original image body as a residual image body 141;.

The composite system including xerographic plate 12, transfer web 17 and image body 14 is next passed to a negative transfer member without separation between the transfer Web 17 and the xerographic plate. At this point, a transfer of the image body occurs in the opposite direction causing redeposition of the preponderance of the image body on the xerographic plate with a formation of a residual image body 1% on the transfer web 1'7. The new image body 14 appears in all respects to be like the original image body bearing the same number ex cept that it is slightly smaller in total amount the difference being the amount of the transferred image body 19 and, except for total amount, is found to. be the full equivalent thereof. Again at transfer member 25, the preponderance of the image body is transferred from the one support member to the other and generally in the order of 6G to'95% and preferably about 89 to 85% of the image body is thus transferred. It is seen therefore that the new image body 19 represents somewhere in the order of 15 to 20% of the original 8i) to 85% which represented image body 14a and thus where 20% transfer used the new image body 19 consists of about 15 to 16% of the original image and where 85% transfer used, image body 19 consists of somewhat under 13% of the original image. Thus, there is formed by this sequence of operations a copy of the original exposure c mprising image body 19 on transfer web 17 with the image body conforming with the pattern of light and shadow directed onto the xerographic plate. There also was left an image body 14 on the xerographic plate which is almost of the original image and therefore is capable of forming successive xerographic prints by the same methods with the successive prints being of almost equal density since the difference between one print and the next will be an image body content of little more than 10% differential. Furthermore, by appropriate adiustment between one cycle of operation and the next cycle of operation a somewhat higher proportion of residual image may be employed in the subsequent steps so that virtually identical xerographic prints can be produced.

According to a further embodiment of the invention, the means and methods herein described can suitably be applied to a continuously operating machine such as, for example, a rotating cylinder machine as is disclosed and illustrated in Figure 5. in this figure is shown diagrammatically a continuously operating machine designed to produce a plurality of multiple copies automatically from a single exposure and development. As illustrated therein, a rotating cylinde 3i. suitably mounted to rotate in the direction indicated by arrow 32, has a photoconductive, insulating layer on at least a portion of its surface, and thus is an electrophotographic member, comparable with member 1 9 in the preceding figures. This cylinder is disposed and adapted to pass successively through a charging station 33, an exposure station 34, a development station 35, a plurality of transfer stations 36, 36a and 36b, and desirably through a cleaning station 37.

The charging, exposing, developing and cleaning stations are conventional in the art of xerography. Thus, for example, the charging station comprises a charging electrode such as a corona electrode 31 operably connected to a positive polarity high voltage source 42. Similarly, the exposure station 34 is conventional and may include a projection lens 43 or other means of imposing a pattern of light and shadow to be recorded on the surface of the xerographic cylinder 31. The development station 35 may comprise suitable means or methods for applying an electroscopic powder or material to the xerographic cylinder and may, for example, be a hopper 45 or other source of xerographic developer positioned and adapted to cascade developer across the surface of the plate to a catching hopper 46. These means, members'and mechanisms are conventionally shielded from light so that the operations of charging, exposing and developing are carried out substantially in the absence of activating radiation.

The transfer station 36, as in the previous embodiments in the invention, comprise suitable electrodes or the like, positioned and disposed to transfer the electroscopically adhering image, first to the surface of a transfer Web 48, and subsequently preferably back to cylinder 31, or to a second surface as illustrated in Figure 3. The transfer station comprises a positive polarity electrode 50, followed subsequently by a negative polarity electrode 51 which may desirably be corona discharge electrodes operatively connected to a positive polarity high voltage source 52 and a negative polarity high voltage source 53. As in' the previous figures, the positive and negative electrodes serve to transfer the image from the xero'gr'aphic cylinder 31 to the transfer web 48 and subsequently, without separation between the web and the cylinder, transfer the major proportion of the image back to the cylinder, leaving only the residual portion on the transfer web. If desired, a last transfer station 36c may be a single unit station having the positive transfer memher but not the second or negative transfer member.

A plurality of such transfer stations may be positioned around the xerog'raphic cylinder, or, if desired, the devices and-mechanisms may be so operated that the cylinemployed as the master for der is successively cycled past a single transfer station unt1l the desired number of copies is produced.

It will be obvious that various mechanisms and forms of apparatus may be employed for operating a process according to the present invention. Thus, for example, the continuous machine, illustrated in Figure 5, may be modified by any of the transfer mechanisms which are appropriate for the previously described embodiments. Similarly, other transfer members may be employed wherein a xerographic image body or the like is transferred successively to and from a transfer web leaving only a residual image body on the web to form the ultimate print. By suitable means known to the art, the electrostatic image may be developed apart from the xerographic cylinder or plate, and the thus developed image may be multiple copies by the means and methods of the present invention. Likewise, various means and methods may be employed to fix the final image body permanently on the transfer Web, including such conventional means and methods as heat or vapor fusing, pressure fixing or the like, or permanent fixing on an adhesive type surface. it is to be understood that these and many other modifications may be employed without departing from the scope of the present invention.

It will be readily apparent that a great many procedural variations may be made within the scope of the present invention in order to produce multiple copies. One or another of these procedural variations may be employed depending upon the particular result desired, and in some instances depending on equipment and devices available. For example, according to one variation an image is formed on a conventional xerographic plate, by the steps of charging, exposing, and developing in the usual manner. Next, the developed image is transferred, according to this invention, to a sheet of bond paper or the like. Following this, a sheet of a special glossy paper is placed face down against the surface image on the bond paper and transfer from the bond paper to the glossy paper is carried out. This first bond paper is removed and replaced by a second one and the two steps of transfer and reverse transfer are carried out between these two paper surfaces. Desirably, this may be accomplished by passing over the two sheets of paper, first a corona discharge of one polarity and second a corona discharge of opposite polarity. Alternatively, a sandwich of the special paper and the bond paper may be placed on a metal surface With the bond paper contacting the metal and a positive polarity corona discharge electrode passed thereover. Without separating the two sheets, this sandwich of paper is turned over and the same corona discharge electrode passed over the paper. By appropriate repetition of this series of steps, the special glossy paper supplies as the idler sheet according to this invention and a plurality of multiple copies may be produced on su cessive sheets of the bond paper. For this purpose a particularly satisfactory paper to serve as the idler sheet is available under the name of Krornekote, and is believed to be a coated paper having a protein binder which has been dried in contact with a'polished surface.

According to another procedural variation, image may be transferred to bond paper and this paper may be placed in contact with a receiving surface such as a bare metal plate or the like. A first transfer step, for example, negative corona transfer of the image to the receiving surface, causes this receiving surface to become the idler member whereupon repeated steps of double transfer to successive sheets of paper will yield satisfactory multiple copies.

in general, best results are accomplished after unusually heavy development of an electrostatic image, and often under these circumstances it is found that the original powder image contains an excessive amount of powder in background areas corresponding to white areas in the original being reproduced. When this is caused by posithe original tive charged powder deposited in such background areas, the defect can be remedied by a first transfer using negative corona discharge. The surface to which this negative corona discharge is made contains a preponderance of the undesired. positively charged powder and may be discarded.

It is to be understood that the invention has been described with reference particularly to the embodiments of xerography in which a photo-conductive insulator is charged to positive polarity and negatively charged powder is deposited thereon to yield an image body. It will be realized that by reversal of polarity the apparatus and methods of this invention may be applied to images of positively charged powder but that alternative discussion of such reversal tends to confuse rather than clarify the illustration. Accordingly, these variations and modifications will be left to those skilled in the art.

By virtue of the present invention, it is now possible to prepare and produce a plurality of xerographic images or prints on a suitable transfer member utilizing only a single charging, exposing and developing cycle for each set of multiple copies. These multiple copies can be produced quickly and easily in a selected number, depending on the number of copies desired.

What is claimed is:

l. The method of forming a plurality of prints from a single original developed xerc-graphic powder particle image comprising electrostatically transferring part of the developed image to a transfer web by applying a first electrostatic field to attract particles to the web and then applying an electrostatic field to repel particles from the web, removing the transfer web carrying thereon the nnrepelled particles conform ng in configuration to the original developed image from the remaining original powder particle image, and ti n through at least one more cycle e'lectrostatically transferring part of the remaining original developed image to another transfer web by again applying a first electrostatic field to attract particles and then an electrostatic field to repel particles and removing the new transfer web carrying thereon the unrepelled particles conforming in configuration to the original developed image from the remaining original powder particle image.

2. The method of forming a plurality of prints from a single original developed xerographic powder particle image body positioned on an image bearing surface of an image carrying layer, said method comprising positioning a transfer web across the original developed image, applying a first electrostatic field to attract sixty to ninetyfive percent of the particle image body to the web and then applying an electrostatic field of polarity opposite to said first electrostatic field to repel sixty to ninety-five percent of the attracted particle image body from the web, removing the transfer web carrying thereon the unrepelled particles conforming in config ration to the original developed image from the remaining original powder particle image, and then through at least one more cycle, positioning a new transfer web across the remaining original powder particle image, applying a first electrostatic field to attract from sixty to ninety-five percent of the remaining image body to the new transfer web and then applying an opposite polarity electrostatic field to repel from sixty to ninety-five percent of the attracted particles from the new transfer web, and removing the new transfer web carrying thereon the unrepelled particles conforming in configuration to the original developed image from the remaining original powder particle image.

3. The method of claim 2 in which the original developed xerographic powder particle image body comprises positively electrostatically charged powder particles and in which the first electrostatic field comprises depositing negative corona discharge across the transfer web to attract image particles to the transfer web.

4. The method of claim 2 in which the original developed xerographic powder particle image body comprises '5 negatively electrostaticarly charged powder particles and in which the first electrostatic field is applied through the deposition of positive corona discharge across the transfer web;

5. The method of forming a plurality of prints from a single original electrostatically charged powder particle image body positioned on an image bearing surface of an image carrying layer, said method comprising forming at least one print by carrying out the following manipulations through at least one cycle: placing a transfer web across the original particle image, applying a first electrostatic field to attract sixty to ninety-five percent of the particle image body to the web and then applying an electrostatic field of polarity opposite to said first field to repel sixty to ninety-five percent of the attracted particle image body from the web, and removing the transfer web carrying thereon the unrepelled particles conforming in configuration to the original particle image from the remaining original powder particle image; and following completion of a desired number of cycles positioning a new transfer web across the remaining original powder particle image, applying an electrostatic field to attract from sixty to ninety-five percent of the remaining image body to the new transfer web, and removing the new transfer web carrying thereon the attracted powder particles conforming in configuration to the original particle image from the residual original powder particle image.

6. Apparatus for forming a plurality of prints from a single image of powder loosely adhering to an image surface of an image layer, said apparatus comprising a supporting for said image layer, means adjacent to said support to feed a transfer surface of a transfer web into contiguous relationship with the image surface of said image layer on said support, first field means adjacent to the support and disposed to operate at a position of contiguous relationship to said image surface and said transfer surface to apply a first electrostatic field between the image surface and the transfer surface, a second field means adjacent to said first field means and in a position of contiguous relationship to the image surface and transfer surface to apply a second electrostatic field of polarity opposite to said first field, and means to cause relative movement between said support and said first and second field means to cause the image layer and transfer web positioned on said support to move first beneath said first field means and then beneath said second field means.

7. Apparatus according to claim 6' in which said first and second field means each comprises a corona dis charge electrode.

8. Apparatus for forming a plurality of prints from a single image of powder loosely adhering to an image surface of an image layer, said apparatus comprising a support adapted to carry thereon said image layer with said image surface against a transfer Web, first field means adjacent to the support and adapted to apply an electrostatic field between the image surface and the transfer web, second field means adjacent tosaid first field means and adapted to apply an electrostatic field between the image surface and the transfer web, a potential source connected to said first field means and said second field means and adapted to apply an electric potential of oppo site polarity to each of said field means, and means to cause relative movement between said support and said first and second field means to cause the image layer and transfer web positioned on said support to move first beneath said first field means and then beneath said second field means.

References Cited in the file of this patent UNITED STATES PATENTS 2,248,064 Carlton et al July 8, 1941 2,576,047 Schaficrt Nov. 20, 1951 2,637,651 Copley May 5, 1953 2,756,676 Steinhilper July 31, 1956 OTHER REFERENCES New Development in XeroradiographyNon-Destructive Testing; Summer 1951, vol. 10, No. 1, pp. 8-25, pp. 10 and 18 particularly relied upon. (Photostat copy in Div. 67.) 

